The present invention relates to a storage system used in a computer system, and particularly to a storage system wherein the placement of data blocks in a file assigned to within the storage system is improved.
In a current computer system, a disk device is used as a secondary storage system and stores therein data necessary for a host device such as a host processor to execute processing. A storage system grows in increasing demand for a great increase in its capacity as the secondary storage system. A secondary storage system such as a RAID increased in capacity by comprising a plurality of physical devices and a control device for controlling the plurality of physical devices and allowing a host device to recognize them as virtual logic devices has appeared. A plurality of devices constituting such a secondary storage system include a disk unit fast in access rate, a device slow in access rate but large in capacity, etc. Further, a storage system in which those different in access rate are mixed, is now commercially available. In order to enhance an average access rate of the whole storage system, these devices select a storage physical device for storing data blocks according to the frequency of access to a file as viewed from the host device and places the same therein. As to the measurement of the access frequency, the number of times of access to a file within a predetermined time, is measured in file units managed by the host device, for example. A file high in access frequency and a logical volume including the file high in access frequency are placed in a storage system high in access rate.